1. Field of the Invention
The present invention relates to a three-group zoom lens and an imaging device, and more particularly to a three-group zoom lens suitable for use in a digital camera, a video camera, and the like, using an imaging element such as a CCD (Charge-Coupled Device) or CMOS (Complementary Metal Oxide Semiconductor), as well as to an imaging device equipped with the three-group zoom lens.
2. Description of the Related Art
In recent years, digital cameras and video cameras become widespread rapidly. In addition to attaining miniaturization, higher image quality, and lower distortion, lenses provided in these cameras are desired to attain cost reduction as are lenses for common cameras. Moreover, in relation to these cameras, a demand exists for an optical zoom system capable of varying power without deterioration of image quality. Demands for zoom-lens-equipped cameras are growing year by year. In these cameras, autofocusing has gone mainstream, and faster focusing is desired.
An inner focusing system or a rear focusing system—which enables a reduction in the weight of a lens, uses a lens positioned closely to a camera main body, and is easy to drive—is frequently used as the focusing system of the zoom lens. In relation to the number of lens groups, a three-group configuration is considered to be more desirable than a two-grouped configuration, because miniaturization and superior correction of aberrations can be accomplished. In JP-A-2007-193140, a zoom lens of three-group configuration which can be applied to a digital camera is proposed.
Moreover, JP-A-2005-321744 describes a compact three-group zoom lens that has accomplished a compact configuration by effective use of aspherical lenses. JP-A-2005-258064 and JP-A-2000-267009 describe zoom lenses which use a plurality of plastic lenses in order to achieve cost reduction and which exhibit a nearly-three-times zoom ratio.
As mentioned above, proliferation of the digital cameras, and the like, is remarkable, and demands for miniaturization, higher performance, and cost reduction of a zoom lens provided in these cameras becomes sterner year by year.
The zoom lens described in JP-A-2005-321744 is very compact, but glass is used for a material of an aspherical lens, which makes the lens expensive and insufficient in terms of cost reduction.
In relation to the zoom lenses described in JP-A-2005-258064 and JP-A-2000-267009, an attempt is made to achieve cost reduction and a reduction in weight by use of a plurality of plastic lenses. However, each of the lens groups has a great thickness, and hence the entire length of a lens system achieved in an optical direction thereof becomes longer when the lens system is retractably housed in a camera main body. Thus, the zoom lenses are insufficient in terms of miniaturization.